The transfer of one or two embryos during IVF should be dependent on the age of the mother, according to a UK study.

Results showed that implanting three or more embryos should be avoided at all ages to prevent adverse effects on the mother and baby before and after birth. However, the prospective study on Human Fertilisation and Embryology Authority (HEFA) data shows the transfer of two embryos may be of overall benefit in women over 40, by increasing the chances of successful fertilisation. These findings have potential implications in the way in which IVF is administered in the future.

Transferring multiple embryos during IVF increases the chances of twin and triplet births, which carry increased health risks to both the mother and babies. After a consultation in 2007, the HFEA introduced a new policy aimed at reducing the multiple birth rate from IVF treatment. The policy came into force in 2009 requiring clinics to have in place a multiple birth minimisation strategy and that they do not exceed a maximum multiple birth rate set by the HFEA.

Researchers at the Medical Research Council in Bristol, led by Professor Debbie Lawlor, quantified the risks and benefits associated with single versus multiple embryo implantations in women younger and older than 40 years. 33,000 live births were analysed from 124,000 IVF cycles from across the UK.

'Our findings provide some support for the transfer of two embryos in women older than 40 years, because the risks of pre-term and low birth weight were lower than those in younger women', explains Professor Lawlor.

Generally women in this age group have lower chances of falling pregnant, and so were less likely to have a twin pregnancy after the implantation of two embryos. The results also showed the implantation of three embryos increased the chances of premature birth in both age groups to such an extent that this approach was deemed inadvisable at any age.

'It doesn't improve the chances of a woman having a healthy baby', says Professor Scott Nelson, co-author of the study at the University of Glasgow.

These findings support the differential implantation of one or two embryos dependent in part on a woman's age, with greater consideration given to implanting two embryos in women over the age of 40 years.

In response the HFEA stated: 'Patients must weigh the chance of a live birth against the risks associated with a twin pregnancy and birth, both for herself and her baby'.

The results are currently under consideration and may affect future HFEA guidelines on IVF. The study was published in the journal the Lancet.

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